Lightweight narrow-kerf high-speed core-sampling systems such as those employed by the mining industry have a tendency while progressing through rock formations to deviate considerable from the vertical. Consequently, deviation of the corehole trajectory from the vertical often becomes excessive, thus necessitating costly remedial measures directed at reducing the corehole deviation to within acceptable limits.
In my U.S. Pat. No. 4,679,636, Method and Apparatus for Coring Rock, is described and illustrated a low-cost lightweight narrow-kerf variable-speed reversible electrically-driven downhole core-sampling system, one variation of which features conveyance of a downhole core-sampling apparatus to and from the bottom of the corehole by means of an electromechanical cable through which is transmitted alternating electric current to downhole electric-power conditioning equipment where alternating current is converted by rectifier means to direct current, voltage and rotational speed are adjusted by transformer means, and direct current is reversed by polarity-switch means so as to power a downhole coresampling apparatus driven by a reversible and variable-speed direct-current electric motor. The method and apparatus described and illustrated in the above patent sought among other functions to solve the dog-leg and corehole deviation problems associated with conventional lightweight narrow-kerf high-speed coring technologies whereas all the threaded connections of the reversible downhole core-sampling apparatus were provided back-out protection by means of a set-screw locking system described in my U.S. Pat. No. 4,548,428, Anti Back-Out Steel Coupling or Nonmetallic Composite Pipe.